Why ya gotta be so mean?

I people watch sometimes. This one specific time, was at the football game on Friday night. This girl who is in my seminary class, (who gets up a lot and talks about how she is having a hard time with the people she thought were her friends) was sitting with these girls who are her "friends". I noticed one of the girls said, "Hey! Let's take a picture!" Then when the girl leaned in to be in the picture, that same girl said, "Oh. I just meant us." Then snapped the picture of her and another girl. The girl from my seminary class was obviously embarrassed. Her face got a little pink and tears filled her eyes.
It really makes me sad how people can ne so rude. I know I'm not perfect and I know that I have been in fault of some of these same actions before, but it breals my heart. This girl, is one of the sweetest girls I know. She also has one of the strongest testimonies. These other girls disregard her, as if she is trash. I'm sure this girl has started to believe she must be trash. She is trying so hard to be a good friend to them and they just don't care.
High school is a place where this situation happens often. It's really sad and It breaks my heart.